Tank car construction using longitudinal curved segments

ABSTRACT

A cylindrical shell for a tank of a railway tank car is made using roll-forming technology and straight longitudinal weld seams. The cylindrical shell has a longitudinal axis and a uniform cross-sectional shape in a plane normal to the longitudinal axis. The cylindrical shell includes a plurality of elongated segments welded together along weld seams extending parallel to the longitudinal axis of the cylindrical shell. Each elongated segment forms a portion of the cross-sectional shape of the shell and is formed by passing a flat piece of metal plate stock material through a roll-forming machine configured to progressively bend the piece of stock material. In one embodiment, exactly three identical elongated segments, each defining an arc of 120 degrees, are welded together along adjacent longitudinal edges to form a cylindrical shell having a circular cross-section.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims benefit of U.S. Provisional Patent Application No. 61/834,174 filed Jun. 12, 2013, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to the construction of rail cars, more particularly tank cars for transporting liquids and gases.

BACKGROUND OF THE INVENTION

Railway tank cars generally comprise a tank supported by a railway undercarriage for rolling transport along a rail line. The tank typically includes an elongated cylindrical shell closed by a pair of end caps fixed at opposite ends of cylindrical shell.

A traditional method of manufacturing the tank's cylindrical shell involves making a plurality of shorter cylinders, and combining the shorter cylinders end-to-end to provide an elongated cylindrical tank shell. Each shorter cylinder is formed by bending a rectangular piece of plate material into a cylinder, and welding the adjoining end edges of the bent plate together. Several of these shorter cylinders are combined end-to-end by circumferential weld seams between adjacent shorter cylinders. An example of this type of tank construction is disclosed in U.S. Pat. No. 8,324,527 (Hybinette et al.). This traditional method is time consuming, involves difficult circumferential welding operations requiring elaborate tooling and fixtures for same, and is plagued by quality control challenges related to out-of-round variation in the shorter cylinders.

In view of these problems, various tank constructions utilizing spiral weld seams have been proposed. For example, spiral weld seems are taught in U.S. Pat. Nos. 4,664,307 (Curry et al.) and 6,875,942 (Coughlin et al.). In such constructions, coiled steel plate is unwound into a strip that is fed into a mill that rotates the strip into an appropriate diameter cylinder and applies a spiral or helical weld seam. The mill is complex, and all fabrication steps for the cylindrical shell must be performed at the same location.

SUMMARY OF THE INVENTION

The present invention provides a new and very economical approach to manufacturing a cylindrical shell for the tank of a railway tank car utilizing roll-forming technology and straight longitudinal weld seams.

In accordance with an embodiment of the present invention, the tank of a railway tank car comprises a cylindrical shell having a longitudinal axis and a uniform cross-sectional shape in a plane normal to the longitudinal axis, wherein the cylindrical shell includes a plurality of elongated segments welded together along weld seams extending parallel to the longitudinal axis of the cylindrical shell. Each elongated segment forms a portion of the cross-sectional shape and is formed by passing a flat piece of metal plate stock material through a roll-forming machine configured to progressively bend the piece of stock material. By way of non-limiting example, the uniform cross-sectional shape may be circular, and each elongated segment may be an arc in the circular cross-section. In one embodiment, exactly three identical elongated segments, each defining an arc of 120 degrees, are welded together along adjacent longitudinal edges to form a cylindrical shell having a circular cross-section.

BRIEF DESCRIPTION OF THE DRAWING VIEWS

The invention will be described in detail below with reference to the accompanying drawing figures, in which:

FIG. 1 is a side elevational view of a tank car formed in accordance with an embodiment of the present invention;

FIG. 2 is an exploded view illustrating a plurality of longitudinal curved segments used to construct a cylindrical shell of the tank car shown in FIG. 1;

FIG. 3 is a cross-sectional view taken generally along the line A-A in FIG. 1;

FIG. 4 is an enlarged detail view of region B in FIG. 3;

FIG. 5 is a schematic view of a roll forming machine for forming the longitudinal curved segments shown in FIG. 2 from flat plate stock; and

FIG. 6 is a flow diagram of a process for manufacturing the cylindrical shell of the tank car.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a railway tank car 10 formed in accordance with an embodiment of the present invention. Tank car 10 generally comprises a tank 12 and a railway undercarriage 14 that supports tank 12 for rolling transport along a rail line. Tank 12 includes a cylindrical shell 16 and a pair of end caps 18 fixed at opposite ends of cylindrical shell 16. Cylindrical shell 16 extends along a longitudinal axis 20. The present invention relates to a novel construction of the cylindrical shell 16.

Reference is made also now to FIGS. 2 and 3. In accordance with the present invention, cylindrical shell 16 includes a plurality of elongated segments 22 welded together along weld seams 24 extending parallel to longitudinal axis 20 of cylindrical shell 16. As shown in FIG. 2, cylindrical shell 16 has a uniform cross-sectional shape in a plane normal to longitudinal axis 20, and each elongated segment forms a portion of the uniform cross-sectional shape. For example, the uniform cross-sectional shape may be circular, and each elongated segment 22 may form an arc in the circular cross-section. As described later below, each elongated segment 22 is formed by passing a flat piece of metal plate stock material through a roll-forming machine configured to progressively bend the piece of stock material into its final form.

In the embodiment depicted in the figures, elongated segments 22 are identical to one another, which is advantageous for production efficiency. Cylindrical shell 16 may comprise exactly three elongated segments 22, and the arc formed by each segment 22 is 120 degrees. However, the number of elongated segments may be as few as two or greater than three.

There are competing design considerations in choosing the number of elongated segments 22. Using fewer segments 22 reduces the number of weld seams 24 needed to assemble the segments into a unitary cylindrical shell 16. However, using fewer segments 22 increases the width requirement of steel plate stock for a given shell diameter, and also imposes greater demand on roll-forming machinery to provide additional angular extent of the formed arc in the case of a circular cross-sectional shape. For example, if two identical segments are used instead of three, each segment must form an arc of 180 degrees. Advantageously, only two weld seams 24 would be required instead of three weld seams, meaning fewer welding operations and a reduction in the total length of weld seam that must undergo quality control inspection. However, this also means that the width of plate stock used to manufacture elongated segments 22 would need to be 50% greater, and further roll-forming stations with wider spacing would be needed in a roll-forming machine to obtain the increased arc angle. As a consequence, the footprint of the roll-forming machine would grow and the material handling machinery used to load plate stock into the roll-forming machine would have to be capable of handling the increased weight of each piece of plate stock material.

Keeping the above considerations in mind, the inventor has determined that using exactly three elongated segments 22, each having an arc of 120 degrees, provides an optimal design for most tank sizes used in conventional railway tank cars. Nevertheless, the invention is not confined to an embodiment comprising exactly three segments 22 each having an arc of 120 degrees.

A method of manufacturing cylindrical shell 16 of railway tank car 10 will now be described with further reference to FIGS. 4-6. An initial step S1 is to provide a plurality of elongated flat pieces 30 of metal plate stock material. Each piece 30 may be rectangular in shape and have a width W calculated based on a desired diameter of cylindrical shell 16 and the number of segments 22 to be used, a length L corresponding to a desired axial length of cylindrical shell 16, and a pair of longitudinal edges 32. By way of non-limiting example, half-inch thick steel plate may be used. One of the longitudinal edges 32 of each piece 30 may be beveled on both sides prior to roll-forming to provide space for weld material.

In step S2, each piece 30 is passed longitudinally through a roll-forming machine 100 comprising a plurality of longitudinally spaced roll-forming stations 102 configured to progressively bend the piece 30 of stock material into an elongated segment 22 having a predetermined cross-sectional configuration, in this illustrative case an arc-shaped configuration. In this manner, a plurality of the arc-shaped elongated segments 22 are formed, each elongated segment having a pair of longitudinal edges 32. The number of stations 102 and their individual configuration will depend on several factors, including the cross-sectional shape and diameter of tank 12, the number of elongated segments 22 used to form cylindrical shell 16, and the thickness of plates pieces 30. In a current embodiment using three elongated segments of ½-inch thick plate to fabricate a circular tank having a diameter of 123½ inches, approximately twenty-two roll-forming stations 102 may be provided to make up roll-forming machine 100.

Step S3 is welding the plurality of elongated segments 22 together along their respective longitudinal edges 32 to make the cylindrical shell. As shown in FIG. 4, a beveled edge of a first elongated segment 22 is arranged adjacent a non-beveled edge of a second elongated segment 22 with a slight clearance between the edges (e.g. a 1/16 inch clearance may be provided). The adjacent longitudinal edges are then welded together to form a weld seam 24. A submerged arc welding process may be used. Further elongated segments 22 may be welded to the joined segments 22 in a similar manner to complete cylindrical shell 16.

Embodiments of the present invention are described in detail herein, however those skilled in the art will realize that modifications may be made. By way of non-limiting example, for certain plate thicknesses, coiled plate material may be unwound and fed into roll-forming machine 100, and the roll-formed segments 22 may be cut to length after roll-forming. Such modifications do not stray from the spirit and scope of the invention.

PARTS LIST

10 Railway tank car

12 Tank

14 Undercarriage

16 Cylindrical shell

18 End caps

20 Longitudinal axis of cylindrical shell

22 Elongated segments

24 Weld seams

30 Pieces of metal plate stock material

32 Longitudinal edge

100 Roll-forming machine

102 Stations of roll-forming machine 

What is claimed is:
 1. A railway tank car comprising a cylindrical shell having a longitudinal axis and a uniform cross-sectional shape in a plane normal to the longitudinal axis, wherein the cylindrical shell includes a plurality of elongated segments welded together along weld seams extending parallel to the longitudinal axis of the cylindrical shell and each elongated segment forms a portion of the uniform cross-sectional shape, and wherein each of the plurality of elongated segments is formed by passing a flat piece of metal plate stock material through a roll-forming machine configured to progressively bend the piece of stock material.
 2. The railway tank car according to claim 1, wherein the plurality of elongated segments are identical to one another.
 3. The railway tank car according to claim 1, wherein the uniform cross-sectional shape is circular, and each elongated segment forms an arc in the circular cross-sectional shape.
 4. The railway tank car according to claim 3, wherein the cylindrical shell includes exactly three of the elongated segments.
 5. The railway tank car according to claim 4, wherein the arc formed by each of the plurality of elongated segments is 120 degrees.
 6. A cylindrical shell of a tank for a railway tank car, the cylindrical shell having a longitudinal axis and a uniform cross-sectional shape in a plane normal to the longitudinal axis, wherein the cylindrical shell includes a plurality of elongated segments welded together along weld seams extending parallel to the longitudinal axis of the cylindrical shell and each elongated segment forms a portion of the uniform cross-sectional shape, and wherein each of the plurality of elongated segments is formed by passing a flat piece of metal plate stock material through a roll-forming machine configured to progressively bend the piece of stock material.
 7. The cylindrical shell according to claim 6, wherein the plurality of elongated segments are identical to one another.
 8. The cylindrical shell according to claim 6, wherein the uniform cross-sectional shape is circular, and each elongated segment forms an arc in the circular cross-sectional shape.
 9. The cylindrical shell according to claim 8, wherein the cylindrical shell includes exactly three of the elongated segments.
 10. The cylindrical shell according to claim 9, wherein the arc formed by each of the plurality of elongated segments is 120 degrees.
 11. A method of manufacturing a cylindrical shell of a railway tank car comprising the steps of: providing a plurality of elongated flat pieces of metal plate material; passing each of the plurality of pieces longitudinally through a roll-forming machine configured to progressively bend the piece of stock material into an elongated segment having a curved cross-sectional configuration, whereby a plurality of the arc-shaped elongated segments are formed, each elongated segment having a pair of longitudinal edges; and welding the plurality of elongated segments together along their respective longitudinal edges to make the cylindrical shell.
 12. The method according to claim 11, wherein the plurality of elongated segments are identical to one another.
 13. The method according to claim 11, wherein the cylindrical shell has a circular cross-sectional shape, and each elongated segment forms an arc in the circular cross-sectional shape.
 14. The method according to claim 13, wherein exactly three of the elongated segments are welded together to make the cylindrical shell.
 15. The method according to claim 14, wherein the arc formed by each of the plurality of elongated segments is 120 degrees. 